Combustion chamber liner for well gas and air burner



Dec. 14, 1965 c. HYDE ETAL COMBUSTION CHAMBER LINER FOR WELL GAS AND AIRBURNER Filed NOV. 3. 1964 United States Patent C) COMBUSTION CHAMBERLINER EUR WELL GAS AND AIR BURNER Collin Hyde, Titlin, and Herbert D.Sheets, Jr., Upper Arlington, Ohio, assignors, by mesne assignments, toChevron Research Company, San Francisco, Calif., a corporation ofDelaware Filed Nov. 3, 1964, Ser. No. 408,609 Claims. (Cl. 10o-64) Thisapplication is a continuation-impart of application Serial No. 165,675filed January 11, 1962, by Collin Hyde and Herbert D. Sheets, Ir., andnow abandoned.

This invention relates to downhole gas and air burners used in petroleumproducing wells and the like to improve production therefrom and moreparticularly this invention relates to improved methods and materialsfor use in lining the combustion chamber of an oil well burner. Thisinvention provides a combustion chamber for an oil well burner made froma castable materialv which will set to form a durable lining capable ofwithstanding very high temperatures and high gas velocities.

In the oil-producing art it is well known to stimulate oil productionfrom a well by placing a down-hole gas and air burner in the well toimprove the recovery characteristics of the oil in the well and thesurrounding formation. The diameter of these burners must be small,usually in the 4range of about three inches to ve inches. The allowableheat transfer rate to the oil from the burner is limited by a value atwhich coking of the oil will occur. For many oils this value is in therange of 10,000 B.t.u. per hour per square foot of burner surface. Sincethe gas and air combusted in the burner cause temperatures in excess of3000 F., the burner must beV supplied with a combustion chamber liningwhich will provide an acceptable heat transfer rate to the oil in thewell. Further, the liner must be capable of withstanding very hard useboth in surface handling by the operating crews and in placement in theWell. The liner is also subjected to high gas velocities during use andtherefore it must be formed of a material and in a manner which will noterode during use. Since the burners are located in a well on the lowerend of a long string of tubing, they must be capable of reliableoperation over periods of a year or more of continuous operation withoutfailure. Thus the combustion chamber line is an extremely critical partof a successful downhole burner.

Therefore, it is a principal object of the present invention to providea method and material for forming a liner for the combustion chamber ofa downhole burner which is capable of withstanding very hightemperatures, which is strong enough to withstand rough use withoutfracturing, and which is durable enough to be of service over extendedperiods of use.

Briefly, the present invention provides a combustion chamber liner for adownhole burner formed of aluminum oxide and calcium aluminate cement.The aluminum oxide of the present invention comprises a special mixtureof bubbled alumina and dense alumina. The bubbled alumina and densealumina of the castable mixture have a particular grainsizedistribution. The bubbled alumina confers insulating qualities tothe liner and the dense alumina provides strength to the liner.Desirable features of castability are also obtained from the mixture.Calcium aluminate cement is a cementing material useful with thealuminum oxide. The aluminum oxide and the calcium aluminate cement aremixed in a preferred ratio to form the liner of the invention. When acorrect proportion of water is mixed with the aluminum oxide and calciumaluminate cement, the mixture may be formed into a variety of shapeswhich, when the 3,223,539 Patented Dec. 14, 1965 ice mixture dries, arecapable of withstanding high temperatures and rough use.

Additional objectives and advantages of the present invention willbecome apparent from the following detailed description read in light ofthe accompanying drawing, which is a part of this specification and inwhich:

FIGURE 1 is a view, partially in section, and illustrates an arrangementof downhole burner apparatus and is useful in better understanding thepresent invention;

FIGURE 2 s a sectional View of a downhole gas and air burner.

FIGURE 3 is a sectional View taken at line 3-3 of FIGURE 2. y

In FIGURE l the general arrangement of a downhole burner and itssupporting apparatus assembled for use in a well are shown. In thisparticular installation, for example, the downhole burner 20 isconnected below producing pump 24 by means of a nipple 25. The oil wellpump 24 is operated by means of sucker rod 19 and is used to pump oil tothe surface. Combustible gas and' air from appropriate sources, such asgas source 26 and air source 27, are flowed to the combustion chamber ofthe burner through appropriate tubing. For example, a gas and air line30 provides a passageway down the well to the combustion chamber of theburner. Surface tubing 28 and 29 connect the gas and air sources to thedownhole burner supply line 30. Valves 31, 32 and 33 are used to controlthe gas and air flow. Gas and air enter the interior of burner 20through a side entry port 18.

The burner 20 may be provided with an exhaust tubing 3S, extending fromthe exhaust section of the burner to the surface. A valve 36 is used toadjust the back pres- Sure on the burner 20. The combustible mixture isignited and is burned in the combustion chamber of the burner. Ignitionmay be accomplished by any suitable meansy such as, for example, byelectrical means generally indicated by the numeral 34. The heat fromthe combustion in the combustion chamber of the downhole burner 20serves to improve the production characteristics of the petroleumVproduct in well 21 and formation 22. As mentioned' above, the rate ofheat flux to the oil must be controlled within acceptable limits or theoil will coke on the exterior of the burner. This can have seriousconsequences and can even tend to plug or damage the well. As is evidentfrom the apparatus assembled in' the Well 21 in FIGURE 1, it is seenthat the combustion chamber of the burner must have a relatively smallVdiameter. This can be better realized when it is pointed out that thediameter of the well 21 inside the casing often' is lessy than 7 or 8inches in diameter and all the tubing and equipment must be containedyin this relatively confined' space.

In FIGURE 2 and FIGURE 3 sectional views illustrate one form of adownhole burner in which the combustion chamber liner for the presentinvention is used. The burner, again represented generally by thenumeral 20, has an ignition system, including a glow plug 40 having asuitable surface electrical connection such as wire 59; The combustiblegas andl air mixture enters the burner through side entry port 18 and isdirected into the combustion chamber 60 through passageways 42 and 43.The pas sageways open into ports 51 and 52 in the combustion chamberliner 62. The combustion chamber liner 62 serves to thermally insulatethe wall 63' of burner 20 and to prevent the skin' temperature frombecoming excesf sivel'y high'. In thisv regard it is usually desirabletolimit the skin temperature of the burner to about 600 F. Sincecombustion temperatures' in the combustion chamber may reach as much as3000lo F. or more, a high degree of insulation is required by arelatively thin liner. The liner 62 may be of any suitable length for aparticular burner. Normally the liner 62 is cast inside the burner metalcasing 63. After the liner has. been dried, it is held in place bysuitable means, such as flange 64. Since the overall diameter of theburner must be kept to a minimum, it is apparent that the combustionchamber liner will be subjected to extreme gas velocity to obtain thedesired rate of heat release. Heat releases of 100,000 to 200,000B.t.u.s per hour are not uncommon in downhole burners of this type.

The present invention provides a castable mixture of aluminum oxide andcalcium aluminate cement, which is used in forming the combustionchamber liner. Aluminum oxide has a chemical formula of A1203. Thepurity of Ya given mixture containing aluminum oxide may vary. Forexample, iron is often an impurity associated with aluminum oxide. Thepurity of A1203 in a mixture suitable for use in the invention should beabove 95%. The aluminum oxide can be melted and formed into a variety ofshapes. For example, the molten alumina can be formed into small bubblesor cooled and ground into hard dense grains. The castable of the presentinvention is comprised partly of dense alumina and bubbled alumina.

The dense alumina of the present invention is a generic term for fusedalumina, sintered or calcined alumina, and crushed or broken bubbledalumina. Fused alumina is prepared by melting A1203 and cooling it intopigs. The pigs are crushed in Crushers resulting in a material havinghard, dense grains. Sintered or calcined alumina is made by heatingA1203 short of its melting point and crushing the resulting product. Thehardness and the density of the grains formed by this process depend onthe sintering temperature and on the purity of the A1203. As is wellknown in the art bubbled alumina is formed by blowing a stream of airthrough molten A1203. Hollow spheres usually in excess of 35 mesh sizeresult when the heated A1203 cools. Crushed or broken bubbles made bythis process may be further reduced in size to form dense alumina.Bubbled alumina has a relatively low thermal conductivity and is a goodinsulator.

The bonding agent for the castable of this invention is preferably ahydraulic setting cement. An example of a hydraulic setting cementparticularly useful in the present invention is calcium aluminatecement. As is well known in the art, there are several compounds of CaOand A1203. A typical calcium aluminate cement often contains uncombinedA1203 in quantities up to 50 percent. Any of the well-known calciumaluminate cements which serve to form a strong bond with the alumina areuseful in the present invention. That is to say, the chemical formula ofthe cement is not critical to the castable of the present invention.

One example of a cement which is usable in the present invention is acement of substantially 18% CaO by weight and 80% A1203 by weight withabout 2% by Weight for impurities. The cement is prepared by sinteringlime and alumina together as is well known in the cement manufacturingart.

Calcium aluminate cement will react with Water to produce a hardcementitious mass. It adheres strongly to alumina oxide and thusproduces a strong concrete. In the present invention the percentage byweight of the cement in the castable should be in the range of 25 to 40%of the castable. A particularly desirable range of the cement in thecastable is from 25 to 30% by Weight.

It has been found that grain size distribution of the dense alumina andbubble size of the bubbled alumina are critical to providing acombustion chamber liner having the required temperature resistance andstrength qualities. Grain sizes may be measured by reference to meshsize. The mesh number gives the number of openings per linear inch ofscreen. Thus a 6 mesh size screen refers to a screen having six equalsize openings per linear inch of screen; 10 mesh size screen to a screenhaving ten equal size openings per linear inch. This manner of referringto screen sizes is well known in the art. In designating the size in thepresent invention then, a designation of minus 14 mesh size refers toparticles which pass a 14 mesh screen, hence particles having a size ofsmaller than 14 mesh. A designation herein of minus 12 mesh size refersto all the material which will pass through a 12 mesh screen. Moresimply stated, minus 12 mesh refers to material with the larger than 12mesh size removed. A designation of 20 mesh size refers to particleshaving a size substantially equal to the 20 mesh screen openings.

Table I below is a standard sizing scale base on a standard 200 meshscreen.

T able I Size Mesh Example Millimeters Microns River gravel.

Pea gravel.

Beach sand.

Fine silt.

The alumina bubbles for the preferred castable mixture of the presentinvention should be relatively pure A1203. It has been discovered thatthe bubbles used in the castable mixture must be minus 12 mesh size inorder to prevent pitting of the liner surface when the liner is cast andused in accordance with the invention. In other words, if the 12 meshand larger portion of the alumina bubbles are left in the castable, theresulting liner surface will pit when subjected to high temperature andhigh [gas velocity. This will result in early failure of the liner. islost when bubbles of larger than minus 12 mesh are used. Therefore, toprovide a durable liner which will withstand very high temperatures, thealumina bubbles utilized should be minus 12 mesh size and 20 mesh size.

In order to retain good insulating qualities in the liner, such as arenecessary to maintain the skin temperature of the outside of thecombustion chamber at a level which will not cause the oil in the wellto coke, the alumina bubbles which pass a 20 mesh screen are not used inthe mixture. Since the insulating capacity of the bubble is largely afunction of wall thickness and interior volume, a bubble size betweenminus 12 and 20 mesh size is a desirable size range. Clearly stated,this means the preferred size alumina bubbles are those which will passa 12 mesh screen but not a 20 mesh screen. It has been found that anacceptable castable mixture may contain in the range of from 30 to 50%by weight of alumina bubbles of the size between minus 12 mesh and 20mesh.

The dense alumina of the castable should be minus 14 mesh size andsmaller. Thus, the dense alumina includes crushed fused alumina, crushedalumina bubbles and sintered or calcined alumina which pass a 14 meshscreen. A portion of the minus 14 mesh dense alumina should also pass a48 mesh screen. Thus the size range of dense alumina for the castablemixture is desirably a combination of minus 14 mesh and minus 48 mesh.Extremely line material is not included in the minus 48 mesh size. Thereshould be a substantial amount of the minus 14 mesh size in the mixturewhich does not pass Further, it has been found that strength the 48 meshscreen. Dense alumina of minus 14 mesh size should be in the castablemixture in an amount of between 20 and 30 percent by weight.

It has been discovered that if, in addition to the dense alumina ofminus 14 mesh size, a substantial portion of the total dense aluminacontent of the castable mixture is minus 325 mesh size, casting of theliner is improved.

This is especially true where vibration is used during the I casting ofliners having particularly delicate shapes to insure distribution of thecastable mixture to all parts of the mold. The very fine grain size aidsin retaining a uniform suspension of the larger sized grains and bubblesin the Wet mixture. It has been found that the castable mixture shouldcontain between 5 and 15% by Weight of minus 325 mesh size densealumina.

An example of a castable mixture which has given superior results whenmolded and used as a combustion chamber liner in downhole burners is setout below in Table II in percentage by Weight of each component.

Table II Percent by weight Alumina bubbles minus 12 mesh size About 36Dense alumina minus 14 mesh size About 27 Dense alumina minus 325 meshsize About 9 Calcium aluminate cement 18% CaO, 80%

A1203 About A castable mixture of the formula of Table II mixed with anappropriate amount of water has set to form a liner having superiorqualities of heat resistance and strength. The mixture was mixed in apropor ratio with Water and allowed to harden. A liner cast from thismixture and used to line a borehole heater has proven adequate inlimiting heat transfer to the oil heated by the heater to an acceptablevalue of 10,000 B.t.u. per hour per square foot of surface.

A refractory liner was produced from a castable of the composition ofTable II and was tested under oil well operating conditions. Therefractory withstood high temperatures and high combustion gasvelocities in a manner superior to all other refractories similarlytested. It is believed that limiting the alumina bubbles to minus 12mesh size is a major factor in giving the refractory a surprisingdurability to hot high velocity gases. The refractory produced from thecastable of the present invention was more durable than any otherrefractory tested. The refractory was also particularly resistant toboth mechanical and thermal shock. This is an important feature for oilwell use.

A castable according to Table II, when mixed in proper proportion withwater, can be poured into molds of a wide variety of shapes and willharden to a concrete which makes an ideal combustion chamber lining. Ithas been found critical to use only alumina bubbles of minus 12 mesh inthe castable when used to form the liner for downhole burner. Whencastables are prepared with bubbles larger than minus 12 mesh, theresulting liner pits when exposed to high temperatures and high volumegas flow across its surface. When this pitting occurs, the skintemperature of the burner can become dangerously high and coking of theoil in the Well can occur causing serious problems. As indicated above,since the burner is located at the end of a long tubing string, whichmay extend 5000 feet or more down a well, the liner cannot be inspectedeasily. It is critical, therefore, to have a liner which is sure to bein top shape for operation over long periods when inspection and repairor replacement cannot be done.

It is desirable to limit the largest size of the dense alumina to minus14 mesh with a substantial portion passing a 325 mesh screen to give theliner mechanical and thermal strength. In a preferred embodiment, thedense alumina passing a 325 mesh screen should be about 9% by weight.The substantial portion of very tine dense alumina insures that phaseseparation between the water and the castable mixture will not occurduring forming of the castable.

To prepare the liner of the present invention by molding, water shouldbe added to the dry castable mixture. A preferred percentage of water toadd to the castable to prepare it for molding is about 10% to 15 waterby weight. A ratio of about 10% water by Weight has given verysatisfactory results. A mixture of the castable and 10% water by weightwill set up in about 24 hours at room temperature to form a liner havingthe special qualities of strength and heat resistance needed for use inwell burners. The mixture should also be oven dried for an additional 24hours at about 150 F. A further period of oven drying at 250 F. for 24hours is also desirable to obtain a refractory with superior qualities.

As is obvious from the above discussion, a castable mixture useful informing a combustion chamber liner having superior qualities is providedherein. A preferred embodiment of the invention having been described,we claim:

1. A method of forming the liner for the combustion chamber of agas-and-air burner comprising the steps of preparing a dry castablemixture of alumina bubbles, between minus 12 mesh and 20 mesh size,about 30 to 50 percent by weight; dense alumina, minus 14 mesh size,about 20 to 30 percent by weight; dense alumina, minus 325 mesh size,about 5 to 15 percent by weight; and calcium aluminate cement, about 25to 40 percent by Weight; mixing said castable mixture with water;molding the wet castable mixture into a predetermined shape to serve asa liner for the combustion chamber of a gas-andair burner; and dryingsaid Wet mixture in said shape.

2. The method of forming a combustion chamber liner comprising the stepsof forming a dry castable mixture of alumina bubbles, between minus 12mesh and 20 mesh size, about 30 to 50 percent by Weight; dense alumina,minus 14 mesh size, about 20 to 30 percent by weight; dense alumina,minus 325 mesh size, about 5 to 15 percent by weight; and calciumaluminate cement, about 25 to 40 percent by Weight; mixing said castablemixture with water; forming the wet castable mixture in a predeterminedshape to serve as a combustion chamber liner; and baking said mixture insaid shape to solidify said mixture in said shape.

3. A new article of manufacture comprising a cornbustible chamber lineressentially consisting of alumina bubbles, between minus 12 mesh and 20mesh size, about 30 to 50 percent by weight; dense alumina, minus 14mesh size, about 20 to 30 percent by weight; dense alumina, minus 325mesh size, about 5 to 15 percent by weight; and calcium aluminatecement, about 25 to 40 percent by weight.

4. A new article of manufacture comprising a combustion chamber linerfor a downhole well burner consisting essentially of alumina bubbles,minus 12 mesh and 20 mesh size, about 36 percent by Weight; densealumina, minus 14 mesh size and minus 325 mesh size, about 36 percent byweight; and calcium aluminate cement, about 28 percent by weight.

5. A combustion chamber liner comprising alumina bubbles, between minus12 mesh and 20 mesh size, about 36 percent by weight; dense alumina,minus 14 mesh size, about 27 percent by weight; dense alumina, minus 325mesh size, about 9 percent by weight; and calcium aluminate cement,about 28 percent by weight.

6. A castable mixture consisting essentially of alumina bubbles, betweenminus 12 mesh and 20 mesh size, about 30 to 50 percent by weight; densealumina, minus 14 mesh size, about 20 to 30 percent by weight; densealumina, minus 325 mesh size, about 5 to 15 percent by weight; andcalcium aluminate cement, about 25 to 40 percent by weight.

7. A composition of matter consisting essentially of alumina bubbles,between minus l2 mesh and 20 mesh size, about 30 to 50 percent byWeight; dense alumina, minus 14 mesh size and minus 48 mesh size, asubstantial portion of which does not pass a 48 mesh screen, about 20 to30 percent by weight; dense alumina, minus 325 mesh size, about 5 to 15percent by Weight; and calcium aluminate cement, about 25 to 30 percentby weight.

8. A castable mixture comprising alumina bubbles, between minus 12 meshand 20 mesh size, about 36 percent by weight; dense alumina, minus 14mesh size and minus 325 mesh size, a total of 36 percent by weight withat least about a 5 to 15 percent by weight portion passing a 325 meshscreen; and calcium aluminate cement, about 28 percent by Weight.

9. A castable mixture comprising alumina bubbles, beminus 12 mesh and 2Omesh size, about 36 percent by weight; dense alumina, minus 14 mesh sizeand minus 48 mesh size, a total of about 27 percent by weight;v

dense alumina, minus 325 mesh size, about 9 percent by Weight; andcalcium aluminate cement, about 28 percent by weight.

10. A castable mixture comprising alumina bubbles, ybetween minus 12mesh and 20 mesh size, about 36 percent by weight; dense alumina, minus14 mesh size, about 27 percent by weight; dense alumina, minus 325 meshsize, about 9 percent by weight; and calcium aluminate cement, about 28percent by weight.

References Cited by the Examiner UNITED STATES PATENTS 2,965,506 12/1960Ueltz 106-64 TOBIAS E. LEVOW, Primary Examiner.

7. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF ALUMINA BUBBLES,BETWEEN MINUS 12 MESH AND 20 MESH SIZE, ABOUT 30 TO 50 PERCENT BYWEIGHT; DENSE ALUMINA, MINUS 14 MESH SIZE AND MINUS 48 MESH SIZE, ASUBSTANTIAL PORTION OF WHICH DOES NOT PASS A 48 MESH SCREEN, ABOUT 20 TO30 PERCENT BY WEIGHT; DENSE ALUMINA, MINUS 325 MESH SIZE, ABOUT 5 TO 15PERCENT BY WEIGHT; AND CALCIUM ALUMINATE CEMENT, ABOUT 25 TO 30 PERCENTBY WEIGHT.